hey man, tell me how it works out. Also, what kind of filter does your intake use? is it K&N or something diffrent, If it's something diffrent PLEASE PLEASE tell me what it is, and where I might procure some of those filters.

Torque0 and I are trying to build our own intake for the 525i, and we cant find a viable alternative filter.

impact on HP is roughly 15, but variant on temperature and speed (in theory, the car moving would suck in colder air than car that is stationary on a dyno). Regardless, you will notice a difference.

Negative effects: K&N filters must be kept oiled. Over time, the oil dries up and they need to be reoiled. It's not hard, but if neglected its filtering abilities are reduced and you run the risk of using unclean air.

Really? Is there a filter out there that can do better? I have yet to hear about one, but maybe there is. 90% is quite awesome and I can't complain. There is a reason that K&N filters always come with a quality CAI or other intake setup.